... where straight continuous lines differentiate (downward) or integrate (upward) with respect to x, and the straight dashed line with respect to the dashed balloon expression. So that the right-hand, triangular network satisfies the chain-rule for differentiation. To fill in the blanks, you need to do the 'dashed' integration, as though the dashed balloon were just a variable like x or u. But actually this too involves the chain rule, so you might like to consider